The power density of an integrated circuit is largely dependent upon the sizes of the circuit components. Thus, as integrated circuit component sizes diminish, power densities increase correspondingly, thereby creating heat dissipation problems which must be resolved. For example, in a mainframe computer, a 10.times.10 mm integrated circuit may dissipate 30W. This is equivalent to a heat flux of 3.times.10.sup.5 W/m.sup.2.
Most integrated circuits have non-uniform power consumption over the surface of the circuit. For instance, in a fully-integrated microprocessor the data path and clock circuits will typically have much higher watt densities than the cache memory circuits. This non-uniform power dissipation generates a corresponding temperature non-uniformity, or temperature gradient, over the surface of the circuit.
Heat transfer across a temperature gradient occurs by a phenomenon called conduction. At the microscopic level, conduction involves the transfer of energy from more energetic molecules to less energetic molecules. At the macroscopic level, conduction involves the transfer of heat from one part of a body at a higher temperature to another part of a body at a lower temperature.
The thermal characteristics of an integrated circuit may affect the operation of the device. That is, many physical properties of semiconductors depend upon temperature. For instance, logic speed, reference voltages, signal propagation delays, and switching thresholds are affected by local temperature conditions.
A variety of approaches exist for removing heat from a semiconductor. One typical approach is to use an adhesive to attach the semiconductor to a heat removal device such as a metallic heat sink or thermosiphon. Care must be exercised during the manufacturing process to insure that no gaps form in the adhesive. Gaps in the adhesive may result in the formation of local hot spots on the semiconductor which may seriously disrupt the semiconductor performance.